Wireless communication method and wireless communication terminal using same

ABSTRACT

The present invention relates to a wireless communication method for suggesting a packet preamble structure for efficient communication in a wireless communication environment in which a legacy terminal and a non-legacy terminal are mixed, and a wireless communication terminal using the same. 
     For this, the present invention provides a wireless communication method including: generating a packet including a first preamble and a second preamble, wherein a first symbol and a second symbol of the second preamble are modulated using binary phase shift keying (BPSK); and transmitting the generated packet and a wireless communication terminal using the same.

TECHNICAL FIELD

The present invention relates to a wireless communication method forsuggesting a packet preamble structure for efficient communication in awireless communication environment in which a legacy terminal and anon-legacy terminal are mixed, and a wireless communication terminalusing the same.

BACKGROUND ART

In recent years, with supply expansion of mobile apparatuses, a wirelessLAN technology that can provide a rapid wireless Internet service to themobile apparatuses has been significantly spotlighted. The wireless LANtechnology allows mobile apparatuses including a smart phone, a smartpad, a laptop computer, a portable multimedia player, an embeddedapparatus, and the like to wirelessly access the Internet in home or acompany or a specific service providing area based on a wirelesscommunication technology in a short range.

Institute of Electrical and Electronics Engineers (IEEE) 802.11 hascommercialized or developed various technological standards since aninitial wireless LAN technology is supported using frequencies of 2.4GHz. First, the IEEE 802.11b supports a communication speed of a maximumof 11 Mbps while using frequencies of a 2.4 GHz band. IEEE 802.11a whichis commercialized after the IEEE 802.11b uses frequencies of not the 2.4GHz band but a 5 GHz band to reduce an influence by interference ascompared with the frequencies of the 2.4 GHz band which aresignificantly congested and improves the communication speed up to amaximum of 54 Mbps by using an OFDM technology. However, the IEEE802.11a has a disadvantage in that a communication distance is shorterthan the IEEE 802.11b. In addition, IEEE 802.11g uses the frequencies ofthe 2.4 GHz band similarly to the IEEE 802.11b to implement thecommunication speed of a maximum of 54 Mbps and satisfies backwardcompatibility to significantly come into the spotlight and further, issuperior to the IEEE 802.11a in terms of the communication distance.

Moreover, as a technology standard established to overcome a limitationof the communication speed which is pointed out as a weak point in awireless LAN, IEEE 802.11n has been provided. The IEEE 802.11n aims atincreasing the speed and reliability of a network and extending anoperating distance of a wireless network. In more detail, the IEEE802.11n supports a high throughput (HT) in which a data processing speedis a maximum of 540 Mbps or more and further, is based on a multipleinputs and multiple outputs (MIMO) technology in which multiple antennasare used at both sides of a transmitting unit and a receiving unit inorder to minimize a transmission error and optimize a data speed.Further, the standard can use a coding scheme that transmits multiplecopies which overlap with each other in order to increase datareliability.

As the supply of the wireless LAN is activated and further, applicationsusing the wireless LAN are diversified, the need for new wireless LANsystems for supporting a higher throughput (very high throughput (VHT))than the data processing speed supported by the IEEE 802.11n has comeinto the spotlight. Among them, IEEE 802.11ac supports a wide bandwidth(80 to 160 MHz) in the 5 GHz frequencies. The IEEE 802.11ac standard isdefined only in the 5 GHz band, but initial 11ac chipsets will supporteven operations in the 2.4 GHz band for the backward compatibility withthe existing 2.4 GHz band products. Theoretically, according to thestandard, wireless LAN speeds of multiple stations are enabled up to aminimum of 1 Gbps and a maximum single link speed is enabled up to aminimum of 500 Mbps. This is achieved by extending concepts of a radiointerface accepted by 802.11n, such as a wider radio frequency bandwidth(a maximum of 160 MHz), more MIMO spatial streams (a maximum of 8),multi-user MIMO, and high-density modulation (a maximum of 256 QAM).Further, as a scheme that transmits data by using a 60 GHz band insteadof the existing 2.4 GHz/5 GHz, IEEE 802.11ad has been provided. The IEEE802.11ad is a transmission standard that provides a speed of a maximumof 7 Gbps by using a beamforming technology and is suitable for high bitrate moving picture streaming such as massive data or non-compression HDvideo. However, since it is difficult for the 60 GHz frequency band topass through an obstacle, it is disadvantageous in that the 60 GHzfrequency band can be used only among devices in a short-distance space.

Meanwhile, in recent years, as next-generation wireless LAN standardsafter the 802.11ac and 802.11ad, discussion for providing ahigh-efficiency and high-performance wireless LAN communicationtechnology in a high-density environment is continuously performed. Thatis, in a next-generation wireless LAN environment, communication havinghigh frequency efficiency needs to be provided indoors/outdoors underthe presence of high-density stations and access points (APs) andvarious technologies for implementing the communication are required.

DISCLOSURE Technical Problem

As described above, an object of the present invention is to providehigh-efficiency/high-performance wireless LAN communication in ahigh-density environment.

Another object of the present invention is to automatically detect aformat of a corresponding packet through information included in apreamble of a wireless LAN packet and distinguish legacy/non-legacypackets.

Another object of the present invention is to provide an efficientsignal processing method in a communication situation between terminalssupporting a plurality of communication methods.

Technical Solution

In order to achieve the objects, the present invention provides awireless communication method and a wireless communication terminal asbelow.

First, an embodiment of the present invention provides a wirelesscommunication terminal including: a transceiver configured to transmitand receive a wireless signal; and a processor configured to control anoperation of the wireless communication terminal, wherein the processorgenerates a packet including a first preamble and a second preamble,wherein a first orthogonal frequency division multiplexing (OFDM) symboland a second OFDM symbol of the second preamble are modulated usingbinary phase shift keying (BPSK), and transmits the generated packet.

In an embodiment, the first preamble may be a legacy preamble and mayinclude a legacy short training field (L-STF), a legacy long trainingfield (L-LTF), and a legacy signal field (L-SIG).

In an embodiment, the second preamble may be a non-legacy preamble andmay include a non-legacy signal field (SIG) composed of a plurality ofSIGs.

In an embodiment, the non-legacy SIG may include a first SIG composed ofthe first OFDM symbol of the second preamble and a second SIG composedof the second OFDM symbol and a third OFDM symbol of the secondpreamble.

In an embodiment, the first SIG may be a repeated L-SIG having at leasta part of information identical to that of an L-SIG of the firstpreamble.

In an embodiment, the second SIG may be a high efficiency signal field A(HE-SIG-A).

In an embodiment, the non-legacy SIG may further include a repeatedHE-SIG-A having at least a part of information identical to that of theHE-SIG-A.

In an embodiment, whether the non-legacy SIG includes the repeatedHE-SIG-A may be indicated based on a modulation scheme used for aspecific OFDM symbol of the second preamble.

In an embodiment, the specific OFDM symbol may include the third OFDMsymbol of the second preamble.

In an embodiment, the non-legacy SIG may further include an HE-SIG-Bafter the second SIG.

In an embodiment, whether the non-legacy SIG further includes theHE-SIG-B may be indicated based on a modulation scheme used for aspecific OFDM symbol of the second preamble.

In an embodiment, the specific OFDM symbol may include the third OFDMsymbol of the second preamble.

In an embodiment, a modulation scheme used for the third OFDM symbol ofthe second preamble may indicate at least one of a configuration and asequence of the second preamble.

In an embodiment, the third OFDM symbol may be modulated using any oneof BPSK, quadrature binary phase shift keying (QBPSK), and quadraturephase shift keying (QPSK).

In an embodiment, the first preamble may further include non-legacyadditional information for a non-legacy terminal.

In an embodiment, the non-legacy additional information may represent awireless LAN communication standard mode used for the packet.

In an embodiment, the non-legacy additional information may indicate atleast one of a configuration and a sequence of the second preamble.

In an embodiment, the non-legacy additional information may representsymbol structure information of a non-legacy OFDM symbol used in aspecific region after a legacy preamble of the packet.

In an embodiment, the OFDM symbol structure information may representcyclic prefix (CP) length information of an OFDM symbol used in thenon-legacy region.

In an embodiment, the non-legacy additional information may berepresented by a predetermined bit field of the first preamble.

In an embodiment, the first preamble may include a first subcarrier setfor a legacy terminal and a second subcarrier set for a non-legacyterminal and the non-legacy additional information may be represented bythe second subcarrier set of the first preamble.

In an embodiment, modulation schemes used for the first OFDM symbol to athird OFDM symbol of the second preamble may represent a wireless LANcommunication standard mode used for the packet.

In an embodiment, when the first OFDM symbol, the second OFDM symbol,and the third OFDM symbol are modulated using BPSK, BPSK, and quadraturebinary phase shift keying (QBPSK) respectively, the packet may be anon-legacy packet.

According to another embodiment of the present invention, there isprovided a wireless communication terminal including: a transceiverconfigured to transmit and receive a wireless signal; and a processorconfigured to control an operation of the wireless communicationterminal, wherein the wireless communication terminal receives a packetthrough the transceiver; and the processor determines whether the packetis a non-legacy packet based on orthogonal frequency divisionmultiplexing (OFDM) symbol information after a legacy signal field(L-SIG) of a legacy preamble of the received packet.

In an embodiment, when a first OFDM symbol after the L-SIG of the packetis a repeated L-SIG having at least a part of information identical tothat of the L-SIG of the packet, the packet may be determined as anon-legacy packet.

In an embodiment, when a first OFDM symbol, a second OFDM symbol, and athird OFDM symbol after the L-SIG of the packet are modulated usingbinary phase shift keying (BPSK), BPSK, and quadrature binary phaseshift keying (QBPSK) respectively, the packet is determined as anon-legacy packet.

In addition, according to an embodiment of the present invention, thereis provided a wireless communication method including: generating apacket including a first preamble and a second preamble, wherein a firstsymbol and a second symbol of the second preamble are modulated usingbinary phase shift keying (BPSK); and transmitting the generated packet.

In addition, according to another embodiment of the present invention,there is provided a wireless communication method including: receiving awireless packet; and determining whether the received wireless packet isa non-legacy packet based on orthogonal frequency division multiplexing(OFDM) symbol information after a legacy signal field (L-SIG) of alegacy preamble of the received wireless packet.

Advantageous Effects

According to an embodiment of the present invention, it is possible toquickly and accurately detect a specific wireless LAN communication modebased on a reception signal in a communication situation betweenterminals supporting a plurality of communication methods duringwireless communication.

In addition, according to an embodiment of the present invention, undera communication situation between terminals supporting a plurality ofcommunication methods during wireless communication, an influence on alegacy terminal is minimized by transmitting and receiving additionalinformation for a non-legacy mode, and it is possible to provide animproved performance to a non-legacy terminal in preparation for thelegacy terminal.

In addition, according to an embodiment of the present invention,unnecessary power waste and data transmission/reception delay may bereduced by performing a quick distinction between legacy packets andnon-legacy packets.

DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram illustrating a wireless LAN system according to anembodiment of the present invention.

FIG. 2 is a diagram illustrating a wireless LAN system according toanother embodiment of the present invention.

FIG. 3 is a block diagram illustrating a configuration of a stationaccording to an embodiment of the present invention.

FIG. 4 is a block diagram illustrating a configuration of an accesspoint according to an embodiment of the present invention.

FIG. 5 schematically illustrates a process in which a STA establishes alink with an AP.

FIG. 6 is a diagram illustrating a structure of an IEEE 802.11ac packetsupporting a legacy wireless LAN mode.

FIG. 7 is a diagram illustrating a comparison of the preamble structuresof IEEE 802.11n, 11a, and 11ac packets.

FIG. 8 is a diagram illustrating a symbol specific modulation scheme ofL-SIG, HT-SIG, and VHT-SIG-A for auto detection between 802.11a/n/acpackets.

FIG. 9 is a diagram illustrating a structure of an IEEE 802.11ax packetaccording to an embodiment of the present invention.

FIG. 10 is a diagram illustrating a comparison between structures of alegacy packet and a non-legacy packet according to an embodiment of thepresent invention.

FIGS. 11 to 13 are diagrams illustrating a preamble structure of anon-legacy packet according to an embodiment of the present invention.

FIGS. 14 to 16 are diagrams illustrating a method of transmitting andreceiving data according to a mixed mode (MM) in an environment in whicha legacy terminal and a non-legacy terminal coexist according to anotherembodiment of the present invention.

FIG. 17 is a diagram illustrating a structure of a non-legacy packetincluding non-legacy additional information according to an embodimentof the present invention.

FIG. 18 is a diagram illustrating a structure of a legacy packetincluding non-legacy additional information according to an embodimentof the present invention.

BEST MODE

Terms used in the specification adopt general terms which are currentlywidely used by considering functions in the present invention, but theterms may be changed depending on an intention of those skilled in theart, customs, and emergence of new technology. Further, in a specificcase, there is a term arbitrarily selected by an applicant and in thiscase, a meaning thereof will be described in a corresponding descriptionpart of the invention. Accordingly, it should be revealed that a termused in the specification should be analyzed based on not just a name ofthe term but a substantial meaning of the term and contents throughoutthe specification.

Throughout this specification and the claims that follow, when it isdescribed that an element is “coupled” to another element, the elementmay be “directly coupled” to the other element or “electrically coupled”to the other element through a third element. Further, unless explicitlydescribed to the contrary, the word “comprise” and variations such as“comprises” or “comprising”, will be understood to imply the inclusionof stated elements but not the exclusion of any other elements.Moreover, limitations such as “or more” or “or less” based on a specificthreshold may be appropriately substituted with “more than” or “lessthan”, respectively.

This application claims priority to and the benefit of Korean PatentApplication Nos. 10-2014-0111018 and 10-2014-0165686 filed in the KoreanIntellectual Property Office and the embodiments and mentioned itemsdescribed in the respective applications, which form the basis of thepriority, shall be included in the Detailed Description of the presentapplication.

FIG. 1 is a diagram illustrating a wireless LAN system according to anembodiment of the present invention. The wireless LAN system includesone or more basic service sets (BSS) and the BSS represents a set ofapparatuses which are successfully synchronized with each other tocommunicate with each other. In general, the BSS may be classified intoan infrastructure BSS and an independent BSS (IBSS) and FIG. 1illustrates the infrastructure BSS between them.

As illustrated in FIG. 1, the infrastructure BSS (BSS1 and BSS2)includes one or more stations STA1, STA2, STA3, STA4, and STA5, accesspoints PCP/AP-1 and PCP/AP-2 which are stations providing a distributionservice, and a distribution system (DS) connecting the multiple accesspoints PCP/AP-1 and PCP/AP-2.

The station (STA) is a predetermined device including medium accesscontrol (MAC) following a regulation of an IEEE 802.11 standard and aphysical layer interface for a radio medium, and includes both anon-access point (non-AP) station and an access point (AP) in a broadsense. Further, in the present specification, a term ‘terminal’ may beused to refer to a non-AP STA, or an AP, or to both terms. A station forwireless communication includes a processor and a transceiver andaccording to the embodiment, may further include a user interface unitand a display unit. The processor may generate a frame to be transmittedthrough a wireless network or process a frame received through thewireless network and besides, perform various processing for controllingthe station. In addition, the transceiver is functionally connected withthe processor and transmits and receives frames through the wirelessnetwork for the station.

The access point (AP) is an entity that provides access to thedistribution system (DS) via wireless medium for the station associatedtherewith. In the infrastructure BSS, communication among non-APstations is, in principle, performed via the AP, but when a direct linkis configured, direct communication is enabled even among the non-APstations. Meanwhile, in the present invention, the AP is used as aconcept including a personal BSS coordination point (PCP) and mayinclude concepts including a centralized controller, a base station(BS), a node-B, a base transceiver system (BTS), and a site controllerin a broad sense.

A plurality of infrastructure BSSs may be connected with each otherthrough the distribution system (DS). In this case, a plurality of BSSsconnected through the distribution system is referred to as an extendedservice set (ESS).

FIG. 2 illustrates an independent BSS which is a wireless LAN systemaccording to another embodiment of the present invention. In theembodiment of FIG. 2, duplicative description of parts, which are thesame as or correspond to the embodiment of FIG. 1, will be omitted.

Since a BSS3 illustrated in FIG. 2 is the independent BSS and does notinclude the AP, all stations STA6 and STA7 are not connected with theAP. The independent BSS is not permitted to access the distributionsystem and forms a self-contained network. In the independent BSS, therespective stations STA6 and STA7 may be directly connected with eachother.

FIG. 3 is a block diagram illustrating a configuration of a station 100according to an embodiment of the present invention.

As illustrated in FIG. 3, the station 100 according to the embodiment ofthe present invention may include a processor 110, a transceiver 120, auser interface unit 140, a display unit 150, and a memory 160.

First, the transceiver 120 transmits and receives a wireless signal suchas a wireless LAN packet, or the like and may be embedded in the station100 or provided as an exterior. According to the embodiment, thetransceiver 120 may include at least one transmit/receive module usingdifferent frequency bands. For example, the transceiver 120 may includetransmit/receive modules having different frequency bands such as 2.4GHz, 5 GHz, and 60 GHz. According to an embodiment, the station 100 mayinclude a transmit/receive module using a frequency band of 6 GHz ormore and a transmit/receive module using a frequency band of 6 GHz orless. The respective transmit/receive modules may perform wirelesscommunication with the AP or an external station according to a wirelessLAN standard of a frequency band supported by the correspondingtransmit/receive module. The transceiver 120 may operate only onetransmit/receive module at a time or simultaneously operate multipletransmit/receive modules together according to the performance andrequirements of the station 100. When the station 100 includes aplurality of transmit/receive modules, each transmit/receive module maybe implemented by independent elements or a plurality of modules may beintegrated into one chip.

Next, the user interface unit 140 includes various types of input/outputmeans provided in the station 100. That is, the user interface unit 140may receive a user input by using various input means and the processor110 may control the station 100 based on the received user input.Further, the user interface unit 140 may perform output based on acommand of the processor 110 by using various output means.

Next, the display unit 150 outputs an image on a display screen. Thedisplay unit 150 may output various display objects such as contentsexecuted by the processor 110 or a user interface based on a controlcommand of the processor 110, and the like. Further, the memory 160stores a control program used in the station 100 and various resultingdata. The control program may include an access program required for thestation 100 to access the AP or the external station.

The processor 110 of the present invention may execute various commandsor programs and process data in the station 100. Further, the processor110 may control the respective units of the station 100 and control datatransmission/reception among the units. According to the embodiment ofthe present invention, the processor 110 may execute the program foraccessing the AP stored in the memory 160 and receive a communicationconfiguration message transmitted by the AP. Further, the processor 110may read information on a priority condition of the station 100 includedin the communication configuration message and request the access to theAP based on the information on the priority condition of the station100. The processor 110 of the present invention may represent a maincontrol unit of the station 100 and according to the embodiment, theprocessor 110 may represent a control unit for individually controllingsome component of the station 100, for example, the transceiver 120, andthe like. The processor 110 controls various operations of wirelesssignal transmission/reception of the station 100 according to theembodiment of the present invention. A detailed embodiment thereof willbe described below.

The station 100 illustrated in FIG. 3 is a block diagram according to anembodiment of the present invention, where separate blocks areillustrated as logically distinguished elements of the device.Accordingly, the elements of the device may be mounted in a single chipor multiple chips depending on design of the device. For example, theprocessor 110 and the transceiver 120 may be implemented while beingintegrated into a single chip or implemented as a separate chip.Further, in the embodiment of the present invention, some components ofthe station 100, for example, the user interface unit 140 and thedisplay unit 150 may be optionally provided in the station 100.

FIG. 4 is a block diagram illustrating a configuration of an AP 200according to an embodiment of the present invention.

As illustrated in FIG. 4, the AP 200 according to the embodiment of thepresent invention may include a processor 210, a transceiver 220, and amemory 260. In FIG. 4, among the components of the AP 200, duplicativedescription of parts which are the same as or correspond to thecomponents of the station 100 of FIG. 2 will be omitted.

Referring to FIG. 4, the AP 200 according to the present inventionincludes the transceiver 220 for operating the BSS in at least onefrequency band. As described in the embodiment of FIG. 3, thetransceiver 220 of the AP 200 may also include a plurality oftransmit/receive modules using different frequency bands. That is, theAP 200 according to the embodiment of the present invention may includetwo or more transmit/receive modules among different frequency bands,for example, 2.4 GHz, 5 GHz, and 60 GHz together. Preferably, the AP 200may include a transmit/receive module using a frequency band of 6 GHz ormore and a transmit/receive module using a frequency band of 6 GHz orless. The respective transmit/receive modules may perform wirelesscommunication with the station according to a wireless LAN standard of afrequency band supported by the corresponding transmit/receive module.The transceiver 220 may operate only one transmit/receive module at atime or simultaneously operate multiple transmit/receive modulestogether according to the performance and requirements of the AP 200.

Next, the memory 260 stores a control program used in the AP 200 andvarious resulting data. The control program may include an accessprogram for managing the access of the station. Further, the processor210 may control the respective units of the AP 200 and control datatransmission/reception among the units. According to the embodiment ofthe present invention, the processor 210 may execute the program foraccessing the station stored in the memory 260 and transmitcommunication configuration messages for one or more stations. In thiscase, the communication configuration messages may include informationabout access priority conditions of the respective stations. Further,the processor 210 performs an access configuration according to anaccess request of the station. The processor 210 controls variousoperations such as wireless signal transmission/reception of the AP 200according to the embodiment of the present invention. A detailedembodiment thereof will be described below.

FIG. 5 is a diagram schematically illustrating a process in which a STAsets a link with an AP.

Referring to FIG. 5, the link between the STA 100 and the AP 200 is setthrough three steps of scanning, authentication, and association in abroad way. First, the scanning step is a step in which the STA 100obtains access information of BSS operated by the AP 200. A method forperforming the scanning includes a passive scanning method in which theAP 200 obtains information by using a beacon message (S101) which isperiodically transmitted and an active scanning method in which the STA100 transmits a probe request to the AP (S103) and obtains accessinformation by receiving a probe response from the AP (S105).

The STA 100 that successfully receives wireless access information inthe scanning step performs the authentication step by transmitting anauthentication request (S107 a) and receiving an authentication responsefrom the AP 200 (S107 b). After the authentication step is performed,the STA 100 performs the association step by transmitting an associationrequest (S109 a) and receiving an association response from the AP 200(S109 b).

Meanwhile, an 802.1X based authentication step (S111) and an IP addressobtaining step (S113) through DHCP may be additionally performed. InFIG. 5, the authentication server 300 is a server that processes 802.1Xbased authentication with the STA 100 and may be present in physicalassociation with the AP 200 or present as a separate server.

FIG. 6 illustrates a structure of an IEEE 802.11ac (hereinafter,referred to as 11ac) packet supporting a legacy wireless LAN mode. Asshown in the drawing, the 11ac packet includes a legacy preamble, a veryhigh throughput (VHT) preamble, and VHT data. The legacy preamble may bedecoded by a conventional wireless LAN terminal such as an IEEE 802.11a(hereinafter, referred to as 11a) terminal, and the 11a terminalprotects the 11ac packet based on the information extracted from thelegacy preamble. On the other hand, the 11ac terminal obtains length (T)information of the corresponding packet from the legacy preamble of the11ac packet, and therefore, the VHT preamble of the 11ac packet (forexample, VHT-SIG) may not include additional information on the lengthof the corresponding packet.

FIG. 7 illustrates a comparison of the preamble structures of IEEE802.11n (hereinafter, referred to as 11n), 11a and 11ac packets using 5GHz band. In FIG. 7, the 11n packet and the 11ac packet representpackets supporting a legacy terminal in a mixed mode (MM) operation,respectively.

As shown in the drawing, the packet 11a is composed of a legacy preambleand legacy data (L-Data). The legacy preamble includes a legacy shorttraining field (L-STF), a legacy long training field (L-LTF), and alegacy signal field (L-SIG). Among them, the L-SIG is modulated usingbinary phase shift keying (BPSK). On the other hand, the 11n/ac packetincludes a legacy preamble as in the 11a packet, and includes theidentifiable information of the 11n/ac terminal as a separate preambleafter the L-SIG (i.e., an HT preamble and a VHT preamble). The 11aterminal extracts rate information and length information included inthe L-SIG of a wireless LAN packet. Based on the extracted information,the terminal regards a portion after the L-SIG as legacy data L-Data anddecodes the portion. The legacy data L-Data is modulated using any oneof BPSK, quadrature binary phase shift keying (QPSK), 16-quadratureamplitude modulation (16-QAM), and 64-QAM.

On the other hand, the 11n packet may be distinguished from the 11apacket (an IEEE 802.11g packet in case of 2.4 GHz band) based on themodulation scheme used for the high throughput (HT) preamble after thelegacy preamble. Referring to FIG. 7, initial symbols 310 n and 320 nconstituting the HT-SIG (e.g., HT-SIG1 and HT-SIG2) of the HT preamblein the 11n packet are modulated using a modulation scheme not used for11a packets, that is, quadrature binary phase shift keying (QBPSK). The11n terminal verifies the modulation scheme used for the first symbol310 after the legacy preamble of a received packet and identifies thatthe corresponding packet is the 11n packet when the first symbol 310 ismodulated using QBPSK. The 11n terminal may additionally check whetheror not the QBPSK modulation scheme is used for the second symbol 320after the legacy preamble of the packet to increase the reliability ofpacket format verification.

In such a manner, the operation of distinguishing the format of acorresponding packet based on the modulation scheme used for thepreamble of the packet is called auto detection. By using the autodetection, the 11n terminal may determine whether the correspondingpacket is an 11n packet before a cyclic redundancy check (CRC) processfor the HT-SIG of the received packet is performed. Therefore, if thereceived packet is not an 11n packet, the 11n terminal may reduce powerconsumption due to unnecessary decoding processes, and reduce a datatransmission/reception delay due to an 11a fallback determination.

In a similar manner, the 11ac packet may be distinguished from the 11apacket and the 11n packet based on the modulation scheme used for theVHT preamble after the legacy preamble. However, the preambleconfiguration of the 11ac packet should minimize the influence on theauto detection process of the 11n terminal described above. That is, itis preferable that a modulation scheme that allows the 11n terminal notto identify the corresponding packet as an 11n packet is used for thefirst symbol 310 c after the legacy preamble in the 11ac packet.Referring to FIG. 7, the first symbol 310 c and the second symbol 320 cafter the legacy preamble in the 11ac packet are modulated using BPSKand QBPSK, respectively. In this case, the first symbol 310 cconstitutes the VHT-SIG-A1 of the VHT preamble and the second symbol 320c constitutes the VHT-SIG-A2 of the VHT preamble.

The 11ac terminal determines whether the corresponding packet is an 11acpacket based on the modulation scheme used for the first symbol 310 andthe second symbol 320 after the legacy preamble of a received packet.That is, the 11ac terminal distinguishes the 11n packet and the non-11npacket based on the modulation scheme used for the first symbol 310 anddistinguishes the 11a packet and the 11ac packet among the non-11npackets based on the modulation scheme used for the second symbol 310.

FIG. 8 illustrates a symbol specific modulation scheme of L-SIG, HT-SIG,and VHT-SIG-A for auto detection between 802.11a/n/ac packets.

First, the L-SIGs of the 11a, 11n and 11ac packets are modulated usingBPSK. The 11a terminal extracts L-SIG information of a received packetand regards the subsequent symbols as data. Therefore, even when the 11nor 11ac packet is received, the 11a terminal identifies the receivedpacket as the 11a packet. The 11a terminal extracts the lengthinformation from the L-SIG of the received packet and performsprotection for the received 11n packet or 11ac packet by deferring thetransmission/reception operation by the corresponding length.

Next, the first symbol 310 n and the second symbol 320 n, that is,HT-SIG, after the L-SIG of the 11n packet are modulated using QBPSK. The11n terminal verifies the modulation scheme used for the first symbolafter the legacy preamble of a received packet and identifies that thecorresponding packet is the 11n packet when the first symbol 310 ismodulated using QBPSK. Here, the modulation scheme may be verifiedthrough the distribution between I/Q channels of the constellationpoints of subcarriers where each data transmission is performed. Also,the 11n terminal may additionally check whether or not the QBPSKmodulation scheme is used for the second symbol after the legacypreamble of the received packet, thereby increasing the reliability ofpacket format verification.

Next, the first symbol 310 c after the L-SIG of the 11ac packet ismodulated using BPSK, and the second symbol 320 c is modulated usingQBPSK. That is, the first symbol 310 c and the second symbol 320 c ofthe VHT-SIG-A of the 11ac packet are modulated using BPSK and QBPSK,respectively. The 11ac terminal determines whether the correspondingpacket is an 11ac packet based on the modulation scheme used for thefirst symbol and the second symbol after the legacy preamble of areceived packet. The 11ac terminal should determine whether thecorresponding packet is an 11n packet through the first symbol so thatit may clearly verify the packet format when QBPSK modulation is usedfor the second symbol.

FIG. 9 illustrates a structure of an IEEE 802.11ax (hereinafter,referred to as 11ax) packet according to an embodiment of the presentinvention. In an embodiment of the present invention, a non-legacywireless LAN mode may represent an IEEE 802.11ax wireless LAN mode, anda legacy wireless LAN mode may represent a wireless LAN mode such as alegacy 11a, 11g, 11n, and 11ac compared to the 11ax. In addition, in thepresent invention, the packet format may represent information on thewireless LAN communication standard mode used in the packet, that is,information on a communication standard mode such as IEEE802.11a/g/n/ac/ax.

Referring to FIG. 9, a non-legacy packet (i.e., an 11ax packet) includesa green field that may be designed with a new packet structureidentifiable only by a non-legacy terminal (e.g., an 11ax terminal)after the legacy preamble. As described above, the legacy preamble mayinclude L-STF, L-LTF, and L-SIG for compatibility with legacy terminals,and the non-legacy packet may include a high efficiency (HE) preambleand HE data after the L-SIG. The HE preamble includes HE-SIGs consistingof at least one SIG (e.g., HE-SIG-1, HE-SIG-2, . . . , HE-SIG-n) fornon-legacy wireless LAN operation, HE-STF and HE-LTFs. Also, variousarrangements such as the number and position of each HE-SIG/STF/LTF inthe HE preamble are possible. In an embodiment of the present invention,the HE preamble may be referred to as a non-legacy preamble. In thiscase, in a situation where legacy packets and non-legacy packetscoexist, there is a need for an HE preamble structure allowingnon-legacy terminals to automatically detect information on non-legacypackets while minimizing the impact on legacy terminals.

FIG. 10 illustrates a comparison between structures of a legacy packetand a non-legacy packet according to an embodiment of the presentinvention. As described above, legacy packets may include IEEE802.11a/g/n/ac packets, and non-legacy packets may represent IEEE802.11ax packets.

As shown in the drawing, the HE preamble of the non-legacy packet iscomposed of a plurality of symbols. In the present invention, a symbolindicates an orthogonal frequency division multiplexing (OFDM) symbol,and one symbol includes an effective OFDM symbol section and a guardinterval section. In addition, in FIG. 10, one symbol of the preamblesection may have a length of 4 us, but the present invention is notlimited thereto, and the length of the symbol may vary depending on thetype of discrete Fourier transform (DFT) used. In the followingembodiments, the first symbol, the second symbol, and the third symbolafter the L-SIG of the non-legacy packet are referred to as a firstsymbol 310 x, a second symbol 320 x, and a third symbol 330 x,respectively. That is, the first symbol 310 x, the second symbol 320 x,and the third symbol 330 x represent the first symbol, the secondsymbol, and the third symbol of the HE preamble, respectively.

Referring to FIG. 10, the HE preamble may be divided into three regionsRegion 1, Region 2, and Region 3 based on the preambles of 11n and 11acpackets. First, the first region (Region 1) is a first region after theL-SIG, and may include two symbols. In the first region, the 11a packetincludes legacy data L-Data, the 11n packet includes HT-SIG, and the11ac packet includes VHT-SIG, respectively. Therefore, data demodulationis performed in the first region of the 11a packet, and HT-SIG andVHT-SIG demodulations are performed in the first regions of the 11npacket and the 11ac packet, respectively. As described above, legacyterminals (e.g., 11n and 11ac terminals) capable of performing autodetection may distinguish 11n and/or 11ac packets based on themodulation scheme used for the symbols in the first region, anddemodulate subsequent packets based on the format of a correspondingpacket, that is, the wireless LAN communication standard mode.

According to an embodiment of the present invention, the first symbol310 x and the second symbol 320 x included in the first region in thenon-legacy packet may be modulated using BPSK, respectively. Throughthis, the non-legacy packet may minimize the influence on the autodetection performance of the legacy terminals, that is, the 11n and 11acterminals. According to an embodiment of the present invention, BPSKmodulation may be used for all the subcarriers of the first symbol 310 xand the second symbol 320 x, but a modulation scheme other than BPSK maybe used for some subcarriers (e.g., subcarriers of even/odd indexes).However, if a different modulation scheme is used for some subcarriers,since the auto detection performance of the 11n/ac terminal is degraded,the use of the different modulation scheme may be allowed only inspecified some ranges.

The second region (Region 2) following the first region (Region 1) mayinclude at least one symbol. In the second region, the 11a packetincludes legacy data L-Data, the 11n packet includes HT-STF, and the11ac packet includes VHT-STF, respectively. Therefore, data demodulationis performed in the second region of the 11a packet as in the firstregion, and an STF detection process is performed in the second regionof the 11n packet and the 11ac packet based on the repetitioncharacteristics of a time domain signal. In this case, the symbols ofthe second region of the 11n packet and the 11ac packet are modulatedusing QPSK.

As in the above-mentioned embodiment, when the symbols of the firstregion of a non-legacy packet, that is, the first symbol 310 x and thesecond symbol 320 x are modulated using BPSK, the 11n and 11ac terminalsmay regard the corresponding packet as the 11a packet. Therefore, themodulation scheme used for the symbol of the second region of a packethas a negligible effect on the auto detection processes of the 11nterminal and the 11ac terminal. Therefore, according to an embodiment ofthe present invention, various modulation schemes may be used for thesymbol of the second region of a non-legacy packet, that is, the thirdsymbol 330 x. For example, modulation such as BPSK, QBPSK or QPSK may beused for the third symbol 330 x of a non-legacy packet. According to anembodiment, the third symbol 330 x of a non-legacy packet may bemodulated using QBPSK. In such a way, when QBPSK having orthogonalcharacteristics with respect to BPSK is used for the modulation of thethird symbol 330 x, the non-legacy packet may be distinguished from the11a/g packet. In this case, the non-legacy terminal verifies that thefirst symbol, the second symbol, and the third symbol after the L-SIG ofa received packet are modulated using BPSK, BPSK, and QBPSK,respectively, so that the non-legacy terminal may identify that thecorresponding packet is a non-legacy packet. However, the auto detectionmethod of a non-legacy terminal in an embodiment of the presentinvention is not limited to this, and the auto detection of a non-legacypacket may be performed based on various embodiments described later.

Next, the third region (Region 3) represents the remaining preamblesection after the second region (Region 2). In the third region, the 11npacket includes HT-LTF, and the 11ac packet includes VHT-LTF andVHT-SIG-B, respectively. The symbols in this region are modulated usingBPSK. According to a further embodiment of the present invention, thethird region of a non-legacy packet may be modulated using QBPSK, whichis distinguished from legacy packets such as 11a/n/ac, and a non-legacyterminal may perform the auto detection of a corresponding packet basedon a modulation scheme used for the third region of a non-legacy packet.That is, the modulation scheme of the third region of a non-legacypacket may be used for packet auto detection and additional informationtransmission of a non-legacy terminal. In this case, at least a part ofthe modulation scheme and the preamble configuration of the first regionand the second region of a non-legacy packet may be set to be identicalto those of the legacy packet.

FIGS. 11 to 13 illustrate a preamble structure of a non-legacy packetaccording to an embodiment of the present invention. According to anembodiment of the present invention, a processor of a terminal generatesa packet according to embodiments described later, and transmits thegenerated packet through a transceiver. In each embodiment of FIGS. 11to 13, the same or corresponding parts as those of the embodiment of theprevious drawings will be omitted.

First, FIG. 11 illustrates an embodiment of a preamble configuration ofa non-legacy packet according to the present invention. Referring toFIG. 11, the non-legacy packet includes a legacy preamble and an HEpreamble 300 a. The HE preamble 300 a includes a high efficiency signalfield (HE-SIG), a high efficiency short training field (HE-STF), and ahigh efficiency long training field (HE-LTF). In an embodiment of thepresent invention, the HE-SIG, the HE-STF, and the HE-LTF may bereferred to as a non-legacy SIG, a non-legacy STF and a non-legacy LTF,respectively.

According to the basic structure of FIG. 11, the HE-SIG may include afirst symbol 310 x, a second symbol 320 x, and a third symbol 330 x.According to the embodiment of FIG. 11, the first symbol 310 x and thesecond symbol 320 x are modulated using BPSK, and the third symbol 330 xis modulated using QBPSK. In this case, the non-legacy packet may bedistinguished from the 11n packet through the first symbol 310 xmodulated using BPSK, and may be distinguished from the 11ac packetthrough the second symbol 320 x modulated using BPSK. In addition, thenon-legacy packet may be distinguished from the 11a/g packet through thethird symbol 330 x modulated using QBPSK. In such a way, the HE-SIG ofthe non-legacy packet may be composed of three or more symbols, and mayfurther include an additional SIG if necessary. A specific embodiment ofthis will be described with reference to FIG. 13.

According to a further embodiment of FIG. 11, the modulation scheme usedfor a specific symbol constituting the HE-SIG may indicate theconfiguration and sequence of the HE preamble 300 a. As described later,a part (e.g., HE-SIG-B) of the configuration of the HE-SIG may beselectively included in the HE preamble 300 a, and according thereto,the length of the HE-SIG is variable. According to one embodiment,whether or not a specific modulation scheme is used for the third symbol330 x may indicate whether the partial configuration is included.According to the embodiment of FIG. 11, when QBPSK modulation is usedfor the third symbol 330 x, the HE-SIG may be composed of three symbolsand followed immediately by the HE-STF. That is, when QBPSK modulationis used for the third symbol 330 x, the fourth symbol of the HE preamble330 a may constitute the HE-STF. However, the embodiment of FIG. 11shows an embodiment for determining the configuration and sequence ofthe HE preamble 300 a, and the present invention is not limited thereto.

FIG. 12 illustrates another embodiment of a preamble configuration of anon-legacy packet according to the present invention. According toanother embodiment of the present invention, the HE-SIG of a non-legacypacket may have a variable length. FIG. 12 shows an HE preamble 300 ahaving an HE-SIG composed of three symbols, and an HE preamble 300 bhaving an HE-SIG composed of two symbols.

The HE-SIG may be set to a variable length according to variousembodiments. As described later, the HE-SIG may be composed of aplurality of SIGs, and the length of HE-SIG may vary depending onwhether an additional SIG is included or not. Also, the HE-SIG may havea variable length depending on the frequency band in which thecorresponding packet is used. For example, the HE preamble 300 b of thenon-legacy packet in the first frequency band (e.g., the 2.4 GHz band)where no 11ac packet is transmitted may include an HE-SIG composed oftwo symbols 310 x and 320 x. According to an embodiment, the firstsymbol 310 x and the second symbol 320 x constituting the HE-SIG of theHE preamble 300 b may be modulated using BPSK and QBPSK, respectively.If the first symbol 310 x and the second symbol 320 x of the HE preamble300 b of a non-legacy packet are modulated in the same manner as the11ac packet, a terminal may determine the non-legacy packet by using thesame auto detection method for 11ac packet in the first frequency band(e.g., the 2.4 GHz band). On the other hand, in the second frequencyband (i.e., the 5 GHz band) in which the 11ac packet is transmitted, theHE-SIG of the HE preamble 300 a of a non-legacy packet may furtherinclude an additional SIG composed of the third symbol 330 x in additionto the HE-SIG used in the HE preamble 300 b in the first frequency band.In this case, the non-legacy terminal can determine the non-legacypacket through the modulation scheme used for the third symbol 330 x ofthe HE preamble 300 a or transmission data of the corresponding symbol.On the other hand, the 11ac terminal receiving the HE preamble 300 a ofthe non-legacy packet may determine that the corresponding packet is notthe 11ac packet through the error occurring in the decoding process ofthe VHT-SIG1.

Moreover, although it is shown in FIG. 12 that the length of the HE-SIGvaries by two symbols or three symbols, the present invention is notlimited thereto and the HE-SIG may be set to a length longer than that.A specific embodiment of this will be described with reference to FIG.13.

FIG. 13 illustrates a preamble configuration of a non-legacy packet inmore detail according to an embodiment of the present invention. Asshown in FIG. 13, the non-legacy packet includes a legacy preamble, anon-legacy preamble (i.e., an HE preamble), and non-legacy data (i.e.,HE data). The legacy preamble includes an L-STF, an L-LTF, and an L-SIG.In addition, the HE preamble includes HE-SIGs composed of at least oneSIG (e.g., HE-SIG-1, HE-SIG-2, . . . , HE-SIG-n), an HE-STF, andHE-LTFs. According to an embodiment of the present invention, theHE-SIGs of the HE preamble may be composed of a plurality of SIGs (e.g.,HE-SIG-1, HE-SIG-2, . . . , HE-SIG-n). More specifically, the HE-SIGsmay include a repeated L-SIG and HE-SIG-A, and additionally include anHE-SIG-B, a repeated HE-SIG-A, and the like.

First, the HE-SIGs may include a repeated L-SIG (i.e., RL-SIG) as thefirst SIG (i.e., HE-SIG-1). The RL-SIG is composed of the first symbolafter the L-SIG, and at least a part of which is identical toinformation of the L-SIG. According to an embodiment of the presentinvention, the non-legacy terminal may automatically detect that thecorresponding packet is a non-legacy packet through the RL-SIG of thereceived packet. That is, when the RL-SIG with repeated information ofthe L-SIG is detected after the L-SIG of the received packet, thenon-legacy terminal may determine that the corresponding packet is anon-legacy packet. According to an embodiment of the present invention,the RL-SIG may be modulated using the same modulation scheme as theL-SIG, i.e., BPSK.

Next, the HE-SIGs may include HE-SIG-A as the second SIG (i.e.,HE-SIG-2). The HE-SIG-A is composed of two symbols and includes anHE-SIG-A1 and an HE-SIG-A2. In this case, the HE-SIG-A may be composedof a second symbol and a third symbol after the L-SIG. According to anembodiment of the present invention, the second symbol and the thirdsymbol constituting the HE-SIG-A may be modulated using BPSK and QBPSK,respectively. As a method for performing the auto detection by thenon-legacy terminal, by verifying that the first symbol, the secondsymbol, and the third symbol after the L-SIG of the received packet aremodulated using BPSK, BPSK, and QBPSK, respectively, it may bedetermined that the corresponding packet is a non-legacy packet.

Meanwhile, according to an embodiment of the present invention, thethird symbol of the HE preamble may be modulated by a scheme other thanQBPSK, and the modulation scheme used for the third symbol may be usedto represent additional information of the non-legacy packet. Forexample, the modulation scheme used for the third symbol of the HEpreamble may represent whether the HE preamble of the non-legacy packetincludes an additional SIG, for example, the HE-SIG-B. The third symbolmay be modulated using one of BPSK, QBPSK, and QPSK. Among them, if thefirst modulation scheme is used, it may indicate that the HE preambleincludes the HE-SIG-B, and if the second modulation scheme differentfrom the first modulation scheme, it may indicate that the HE preambledoes not include the HE-SIG-B. According to an embodiment, the thirdsymbol may be modulated using QPSK when the HE preamble includes theHE-SIG-B, and the third symbol may be modulated using QBPSK when the HEpreamble does not include the HE-SIG-B. Thus, when the third symbol ismodulated using QBPSK, the HE-STF in the HE preamble may immediatelyfollow the HE-SIG-A (or repeated HE-SIG-A). However, in the presentinvention, the specific configuration of the HE preamble according tothe modulation scheme of the third symbol is not limited thereto and maybe implemented in the opposite embodiment or another embodiment. Thatis, the third symbol may be modulated using QBPSK when the HE preambleincludes the HE-SIG-B, and the third symbol may be modulated using BPSKwhen the HE preamble does not include the HE-SIG-B.

Next, the HE-SIGs may additionally include repeated HE-SIG-A (i.e.,RHE-SIG-A). The RHE-SIG-A is composed of two symbols, and includes anRHE-SIG-A1 and an RHE-SIG-A2. The RHE-SIG-A1 is set to have at least apart of information identical to that of the HE-SIG-A1, and theRHE-SIG-A2 is set to have at least a part of information identical tothat of the HE-SIG-A2. In addition, the HE-SIG may further include theHE-SIG-B. The HE-SIG-B is composed of at least one symbol and has avariable length. According to an embodiment of the present invention,the HE-SIG may selectively include the RHE-SIG-A and/or the HE-SIG-B. Inthis case, information on at least one of whether or not the RHE-SIG-Ais included in the HE-SIG and whether or not the HE-SIG-B is included inthe HE-SIG may be indicated through the modulation scheme used for aspecific symbol of the HE preamble, for example, the modulation schemeused for the third symbol of the HE preamble.

As taken together with the above-described embodiments, the HE-SIGs ofthe present invention may be modified into the following types ofconfigurations (i.e. elements) and sequences. Hereinafter, the fourthsymbol, the fifth symbol and the sixth symbol indicate the fourthsymbol, the fifth symbol and the sixth symbol after the L-SIG of thenon-legacy packet, respectively.

1) In case that the HE-SIG includes the RL-SIG and the HE-SIG-A. TheHE-SIGs are composed of three symbols and include the RL-SIG (i.e.,first symbol), the HE-SIG-A1 (i.e., second symbol) and the HE-SIG-A2(i.e., third symbol).

2) In case that the HE-SIG includes the RL-SIG, the HE-SIG-A, and theRHE-SIG-A. The HE-SIGs are composed of five symbols, and the followingtwo types are possible. 2-1) the RL-SIG (i.e., first symbol), theHE-SIG-A1 (i.e., second symbol), the HE-SIG-A2 (i.e., third symbol), theRHE-SIG-A1 (i.e., fourth symbol), and the RHE-SIG-A2 (i.e., fifthsymbol). 2-2) the RL-SIG (i.e., first symbol), the HE-SIG-A1 (i.e.,second symbol), the RHE-SIG-A1 (i.e., third symbol), the HE-SIG-A2(i.e., fourth symbol), and the RHE-SIG-A2 (i.e., fifth symbol).

3) In case that the HE-SIG includes the RL-SIG, the HE-SIG-A, and theHE-SIG-B. The HE-SIGs have variable length and include the RL-SIG (i.e.,first symbol), the HE-SIG-A1 (i.e., second symbol), the HE-SIG-A2 (i.e.,third symbol), and the HE-SIG-B (i.e., fourth+ symbol).

4) In case that the HE-SIG includes the RL-SIG, the HE-SIG-A, theRHE-SIG-A, and the HE-SIG-B. The HE-SIGs have variable length, and thefollowing two types are possible. 4-1) the RL-SIG (i.e., first symbol),the HE-SIG-A1 (i.e., second symbol), the HE-SIG-A2 (i.e., third symbol),the RHE-SIG-A1 (i.e., fourth symbol), the RHE-SIG-A2 (i.e., fifthsymbol), and the HE-SIG-B (i.e., sixth+ symbol). 4-2) the RL-SIG (i.e.,first symbol), the HE-SIG-A1 (i.e., second symbol), the RHE-SIG-A1(i.e., third symbol), the HE-SIG-A2 (i.e., fourth symbol), theRHE-SIG-A2 (i.e., fifth symbol), and the HE-SIG-B (i.e., sixth+ symbol).

The HE preamble may include the HE-SIGs in the type described above andthe HE-STF and the HE-LTF, which follow the HE-SIGs. As described above,the HE preamble of the non-legacy packet may have any one of a pluralityof types of configurations and sequences. According to an embodiment ofthe present invention, the configuration and/or sequence of the HEpreamble may be indicated through a modulation scheme used for aspecific symbol of the HE preamble, for example, a modulation schemeused for the third symbol of the HE preamble.

On the other hand, referring to FIG. 13, a symbol structure (e.g., OFDMNumerology) different from that of the legacy preamble may be used forthe HE preamble and the HE data of the non-legacy packet. Here, thesymbol structure indicates the lengths of the effective OFDM symbolsection and the guard interval (or cyclic prefix) section, thesubcarrier spacing of the OFDM signal, the number of guard carriers, andthe number of FFT points used for OFDM symbol configuration, and thelike. As described above, each symbol constituting a packet includes aneffective OFDM symbol section and a guard interval (or cyclic prefix)section. In this case, it is preferable that a relatively long cyclicprefix (CP) is used in a channel environment having a large delay spreadas in the outdoor, and a relatively short CP is used in a channelenvironment having a small delay spread as in a room.

In the case of a legacy symbol used in legacy packets such as11a/g/n/ac, one symbol is composed of an effective OFDM symbol(L-effective OFDM symbol) of 3.2 us and a CP (i.e., L-CP) of 0.8 us or0.4 us. That is, the legacy symbol has a CP overhead of about 20%(=0.8/4.0) or 11.1% (=0.4/3.6) based on the OFDM symbol length of 4 usor 3.6 us. However, the non-legacy symbol used in the non-legacy packetmay set the length of the effective OFDM symbol section to be long whilemaintaining a similar length of the CP section, thereby reducing the CPoverhead. To this end, the non-legacy terminal may implement it byreducing the subcarrier spacing of the OFDM signal used for the HEpreamble of the non-legacy packet. For example, if a subcarrier spacingof 78.125 kHz through 256 FFT is used instead of a subcarrier spacing of312.5 kHz through the existing 64 FFT, the length of the effective OFDMsymbol (i.e., HE-effective OFDM symbol) section of the non-legacy symbolwill have 12.8 us (=3.2 us*4) that is increased by 4 times. In thiscase, the length of the CP (i.e., HE-CP) section of the non-legacysymbol may be set to any one of 0.4/0.8/1.6/3.2/6.4 us, and the lengthof the non-legacy symbol including the effective OFDM symbol section maybe set to any one of 13.2/13.6/14.4/16/19.2 us. Therefore, each CPoverhead of the non-legacy symbol is 3.03/5.88/11.1/20/33.3%, which mayprovide the data throughput improvement effect by up to about 17%compared with the legacy symbol.

According to an embodiment of the present invention, a legacy symbolstructure is used for the symbols of the HE-SIG in the HE preamble of anon-legacy packet, and a non-legacy symbol structure different from thelegacy symbol structure may be used for the symbols from the HE-STFafter the HE-SIG. According to an embodiment, the non-legacy packet mayindicate at least some information (e.g., length information of the CPsection) of the non-legacy symbol structure through additionalinformation of the legacy preamble. A specific embodiment relating tothis will be described later.

FIGS. 14 to 16 illustrate a method of transmitting and receiving dataaccording to a mixed mode (MM) in an environment in which a legacyterminal and a non-legacy terminal coexist according to anotherembodiment of the present invention.

First, FIG. 14 shows a situation of transmitting and receivinguplink/downlink packets between a non-legacy AP and a non-legacy STA.Referring to FIG. 14, STA-1, STA-2, and STA-3 are associated with BSS-1operated by AP-1. Among them, the AP-1 and the STA-3 are non-legacyterminals, and the STA-1 and the STA-2 are 11ac and/or 11n terminals,respectively, which are legacy wireless LAN modes. In the embodiment ofFIG. 14, the non-legacy terminal AP-1 and STA-3 transmit and receivenon-legacy packets. In FIG. 14, a solid line arrow indicates anon-legacy downlink packet transmitted from the AP-1 to the STA-3, and adotted arrow indicates a non-legacy uplink packet transmitted from theSTA-3 to the AP-1.

When the AP-1 and the STA-3 transmit and receive non-legacy packets,corresponding packets may also be received by the STA-1 and the STA-2.However, since the legacy terminals STA-1 and STA-2 are not able toidentify the non-legacy wireless LAN mode, they identify thecorresponding packets in a predetermined wireless LAN mode. That is, theSTA-1 and the STA-2 identify the corresponding packets as 11a/g packetsbased on the preamble information of the received non-legacy packet andoperate in a fallback mode.

According to an embodiment of the present invention, in such a mixedmode, additional information for non-legacy terminals (hereinafter,non-legacy additional information) may be included in non-legacy packetsin order for effective data transmission and reception of non-legacyterminals. According to an embodiment, the non-legacy additionalinformation may be included in the legacy preamble of a non-legacypacket. In FIG. 14, a solid line block arrow indicates that a terminalreceiving a non-legacy packet is able to decode the non-legacyadditional information included in the corresponding packet, and thedotted block arrow indicates that the terminal is not able to decode thenon-legacy additional information. As shown in the drawing, thenon-legacy terminals AP-1 and STA-3 obtain non-legacy additionalinformation included in the non-legacy packet, and perform datatransmission/reception using the non-legacy additional information.However, the legacy terminals STA-1 and STA-2 may not identify thenon-legacy additional information included in the non-legacy packet andthere is no change in the operation of the existing legacy wireless LANmode.

Next, FIG. 15 shows a situation in which the non-legacy AP transmitsdownlink packets to the legacy STA. Referring to FIG. 15, STA-1, STA-2,and STA-3 are associated with BSS-2 operated by AP-2. Among them, theAP-2 and the STA-3 are non-legacy terminals, and the STA-1 and the STA-2are 11ac and/or 11n terminals, respectively, which are legacy wirelessLAN modes. In the embodiment of FIG. 15, the non-legacy terminal AP-2transmits a legacy packet in order for communication with the legacyterminal STA-1. A solid line arrow shown in FIG. 15 indicates an 11acpacket transmitted from the AP-2 to the STA-1.

When the AP-2 transmits an 11ac packet to the STA-1, the correspondingpacket may also be received by the STA-2 and the STA-3. However, sincethe STA-2, which is the 11n terminal, is not able to identify the 11acpacket, it identifies the received packet as the 11a/g packet andoperates in a fallback mode. Meanwhile, the non-legacy terminal STA-3may identify the 11ac packet, and also extract non-legacy additionalinformation when the corresponding packet includes the non-legacyadditional information. Therefore, according to an embodiment of thepresent invention, when a non-legacy terminal transmits a packet to alegacy terminal, it may transmit a legacy packet including non-legacyadditional information. According to an embodiment of the presentinvention, the non-legacy additional information may be included in thelegacy preamble of a legacy packet. In FIG. 15, a solid line block arrowindicates that a terminal receiving a legacy packet is able to decodethe non-legacy additional information included in the correspondingpacket, and a dotted block arrow indicates that the terminal is not ableto decode the non-legacy additional information. As shown in thedrawing, the STA-3, which is a non-legacy terminal, obtains non-legacyadditional information included in the legacy packet, and performs datatransmission/reception using the non-legacy additional information.However, the legacy terminals STA-1 and STA-2 may not identify thenon-legacy additional information included in the legacy packet andthere is no change in the operation of the existing legacy wireless LANmode.

Next, FIG. 16 shows a situation in which the non-legacy STA transmitsuplink packets to the legacy AP. Referring to FIG. 16, STA-1, STA-2, andSTA-3 are associated with BSS-3 operated by AP-3, and STA-4 isassociated with BSS-4 operated by AP-4. Among them, the AP-4, the STA-3,and the STA-4 are non-legacy terminals, and the STA-1 and the STA-2 are11ac and/or 11n terminals, respectively, which are in legacy wirelessLAN modes. In addition, the AP-3 is a legacy terminal, and indicates aterminal in any one of 11a/g/n/ac wireless LAN modes. In the embodimentof FIG. 16, the non-legacy terminal STA-3 transmits a legacy packet inorder for communication with the legacy terminal AP-3. A solid linearrow shown in FIG. 16 indicates any one of 11a/g/n/ac packetstransmitted from the STA-3 to the AP-3.

When the STA-3 transmits a legacy packet to the AP-3, the correspondingpacket may also be received by the adjacent terminals, i.e., the STA-1,the STA-2, the STA-4, the AP-4, and so on. When the non-legacy terminalSTA-3 transmits a legacy packet including non-legacy additionalinformation as in the embodiment of FIG. 15, the non-legacy terminalsAP-4 and STA-4 may obtain the non-legacy additional information includedin the received packet. The non-legacy terminals may perform datatransmission/reception by using the obtained information.

FIG. 17 illustrates a structure of a non-legacy packet includingnon-legacy additional information according to an embodiment of thepresent invention. According to an embodiment of the present invention,a processor of a non-legacy terminal may generate non-legacy packetsaccording to the embodiment of FIG. 17 and transmit the generatedpackets through a transceiver. The non-legacy packet according to theembodiment of FIG. 17 may be used for data communication between thenon-legacy terminals as in the scenario of FIG. 14.

Referring to FIG. 17, the non-legacy terminal generates a non-legacypacket including a legacy preamble and a non-legacy preamble (i.e., HEpreamble), and transmits the generated packet. As described above, thelegacy preamble includes the L-STF, the L-LTF, and the L-SIG, and isidentifiable by legacy terminals including 11a/g terminals. According tothe embodiment of FIG. 17, non-legacy additional information fornon-legacy terminals may be further included in the legacy preamble ofthe non-legacy packet transmitted by the non-legacy terminal. Thenon-legacy additional information may be extracted and decoded by thenon-legacy terminals but is unidentifiable information in the legacyterminals. According to an embodiment of the present invention, thenon-legacy additional information included in the legacy preamble of thenon-legacy packet may include at least one of the following listedinformation.

1) Non-legacy wireless LAN mode (i.e., 11ax) indicator. First, thenon-legacy additional information may include the wireless LANcommunication standard mode information used in the correspondingpacket. When the non-legacy additional information of the receivedpacket indicates a non-legacy wireless LAN mode, the non-legacy terminalmay omit or simplify the auto detection process for determining whetherthe received packet is one of legacy wireless LAN modes, that is,11a/g/n/ac. According to an embodiment of the present invention, thenon-legacy additional information of the legacy preamble may include therepeated L-SIG (i.e., RL-SIG) described above in FIG. 13. The non-legacypacket may include an RL-SIG set to have at least a part of informationidentical to that of the L-SIG of the legacy preamble. The non-legacyterminal may identify that the corresponding packet is a non-legacypacket through the detection of the RL-SIG. When the informationindicating that the received packet is a non-legacy wireless LAN packetis extracted through the legacy preamble of the corresponding packet,the non-legacy terminal can immediately process the area after thelegacy preamble of the received packet in the non-legacy wireless LANmode.

2) Symbol structure (e.g. OFDM Numerology) of non-legacy symbols. Next,the non-legacy additional information may include symbol structureinformation of a non-legacy symbol used in a specific area after thelegacy preamble. As described above, a symbol structure (e.g., OFDMNumerology) different from that of a legacy preamble may be used for thenon-legacy preamble and non-legacy data of a non-legacy packet. Here,the symbol structure indicates the lengths of the effective OFDM symbolsection and the guard interval (or cyclic prefix) section, thesubcarrier spacing of the OFDM signal, the number of guard carriers, andthe number of FFT points used for OFDM symbol configuration, and thelike. According to an embodiment, the non-legacy packet may indicate atleast some information (e.g., length information of the CP section) ofthe non-legacy symbol structure through non-legacy additionalinformation. In such a way, when the non-legacy symbol structureinformation is extracted through the legacy preamble of the non-legacywireless LAN packet, the non-legacy terminal may quickly set the OFDMsymbol synchronization, the FFT size, and the length of CP section fast,thereby reducing the implementation complexity of the non-legacyterminal.

3) Configuration and/or sequence information of non-legacy preamble.Next, the non-legacy additional information may include informationindicating at least one of a configuration (i.e. elements) and sequenceof a non-legacy preamble. As described above with reference to FIG. 13,the configuration and sequence in the non-legacy preamble of thenon-legacy packet may be modified into various forms. According to anembodiment of the present invention, the structure information of anon-legacy preamble may be delivered through the non-legacy additionalinformation of a legacy preamble. For example, the non-legacy additionalinformation may indicate the number of symbols constituting the HE-SIGof the non-legacy preamble. In this case, the non-legacy terminal mayimmediately perform a decoding process such as CRC check based on theobtained symbol number information. Accordingly, the non-legacy terminalmay reduce unnecessary operations such as blind decoding and autodetection, thereby reducing power consumption and obtaining non-legacywireless LAN information more quickly. In addition, non-legacyadditional information may provide various information to supporteffective operations of the non-legacy terminal. The various informationmay include information on the number of symbols constituting the HE-STFand the HE-LTF of a non-legacy preamble, the presence or absence ofadditional SIGs (e.g., HE-SIG-B and RHE-SIG-A), and a method foranalyzing bit information of each configuration of a non-legacypreamble.

4) Additional information for Clear Channel Assessment (CCA) operationof non-legacy terminal. Next, the non-legacy additional information mayinclude a parameter for the CCA operation of a non-legacy terminal orinformation for setting the parameter. According to a further embodimentof the present invention, a CCA threshold value (i.e., first CCAthreshold) used for the CCA operation of a non-legacy terminal may beset to have a higher level than a CCA threshold value (i.e., second CCAthreshold) used for the CCA operation of a legacy terminal. Thenon-legacy terminal may set the CCA threshold value based on thespecific information of the received packet, for example, the BSSidentifier information. Here, the BSS identifier information mayindicate the BSSID or its abbreviated information. According to anembodiment, when the BSS identifier information of the received packetis same as the BSS identifier information of the corresponding terminal,the non-legacy terminal performs a CCA operation using the second CCAthreshold value. When the BSS identifier information of the receivedpacket is different from the BSS identifier information of thecorresponding terminal, the non-legacy terminal may perform a CCAoperation using the first CCA threshold value higher than the second CCAthreshold value. In this case, the BSS identifier information of thereceived packet may be extracted from the non-legacy additionalinformation.

Also, according to another embodiment of the present invention, thenon-legacy additional information may include additional information forsetting the CCA operation of the non-legacy terminal. That is, thenon-legacy additional information may include information indicatingwhether the CCA operation of the non-legacy terminal is performed in thesame manner as the CCA operation of the legacy terminal or is performedby using a new parameter. In this case, information for setting a newparameter may be included in the HE-SIG of the non-legacy preamble. Forexample, the BSS identifier information may be included in the HE-SIG ofthe non-legacy preamble. In addition, an indicator of whether the CCAthreshold value for the CCA operation of the non-legacy terminal to beset based on the BSS identifier information or to be set as the legacyCCA threshold value may be included in the non-legacy additionalinformation of the legacy preamble. According to another embodiment ofthe present invention, the non-legacy additional information may includeoffset information for a CCA Signal Detection (SD)/Energy Detection (ED)threshold value, and the non-legacy terminal may extract the offsetinformation to perform the CCA operation more quickly.

5) Bandwidth extension and channel allocation information. Finally, thenon-legacy additional information may include bandwidth extensioninformation or channel allocation information for non-legacy terminalsperforming orthogonal frequency division multiple access (OFDMA)transmission or transmission through a continuous/non-continuousexpanded bandwidth. According to an embodiment, when a packet istransmitted through a broadband channel where a plurality of channelsare combined, the non-legacy additional information of a packettransmitted through a specific channel may indicate information onanother channel combined with the corresponding channel. For example,when a packet is transmitted with a bandwidth of 40 MHz, non-legacyadditional information included in the packet of 20 MHz band mayindicate the position of another 20 MHz band. In addition, when a packetis transmitted with a bandwidth of 60 MHz, the non-legacy additionalinformation may represent information on the configuration of the 60 MHzoccupying band among the entire 80 MHz available band by using a bit mapor a look-up table. In addition, according to a further embodiment, thenon-legacy additional information includes new primary channel/secondarychannel information such as an alternative primary channel used in thenon-legacy terminal, thereby supporting various bandwidth configurationsof the non-legacy terminal.

According to an embodiment of the present invention, the non-legacypacket may include at least one of the above-mentioned 1) to 5) asnon-legacy additional information. According to an embodiment, thenon-legacy additional information is represented by a predetermined bitfield of the legacy preamble of the non-legacy packet. Morespecifically, the L-SIG of the legacy preamble includes a rate field anda length field, and the non-legacy additional information may berepresented by a combination of specific bit information not used in thelegacy terminal among the fields. For example, in the legacy packet, thelength field of the L-SIG may be set to a value of multiple of 3. Inthis case, the length field of the L-SIG may be set to include a valueother than a multiple of 3 in the non-legacy packet to representnon-legacy additional information. According to an embodiment, thelength of the CP section of the non-legacy symbol may be determined tobe one of three values (e.g., 0.8 us, 1.6 us, and 3.2 us), and theresult value of modulo operation of the length field may indicate anyone of the three values. In this case, the length of the selected CPsection may be applied to the symbols of the HE-STF and the HE-LTF ofthe non-legacy preamble.

According to another embodiment of the present invention, the non-legacyadditional information is represented by an additional subcarrier of thelegacy preamble of the non-legacy packet. According to an embodiment ofthe present invention, the legacy preamble of the non-legacy packet mayinclude a first subcarrier set for the legacy terminal and a secondsubcarrier set for the non-legacy terminal. In this case, the secondsubcarrier set includes a plurality of subcarriers added to the guardband region of the first subcarrier set used in the legacy packet, andmay be identified by the non-legacy terminal but may not be identifiedby the legacy terminal. The non-legacy packet may represent thenon-legacy additional information through the second subcarrier set ofthe legacy preamble, and the corresponding information may be extractedand decoded by the non-legacy terminal. Meanwhile, although thenon-legacy additional information listed above is described as beingincluded in the legacy preamble, the present invention is not limitedthereto, and at least some of them may be included in the non-legacypreamble.

FIG. 18 illustrates a structure of a legacy packet including non-legacyadditional information according to an embodiment of the presentinvention. According to an embodiment of the present invention, aprocessor of a non-legacy terminal may generate legacy packets accordingto the embodiment of FIG. 18 and transmit the generated packets througha transceiver. The legacy packet according to the embodiment of FIG. 18may be used as a packet transmitted from the non-legacy terminal to thelegacy terminal as in the scenario of FIGS. 15 and 16. In the embodimentof FIG. 18, the same or corresponding parts as those of the embodimentof FIG. 17 will be omitted.

According to an embodiment of the present invention, a non-legacyterminal generates legacy packets including non-legacy additionalinformation and transmits the generated packets. The legacy packetincludes packets of 11a/g/n/ac. If the legacy packet is an 11n/acpacket, the corresponding packet includes a first legacy preamble and asecond legacy preamble as shown in FIG. 18. Here, the first legacypreamble indicates the preamble of an 11a/g packet including the legacypreamble in the above embodiment, i.e., the L-STF, the L-LTF, and theL-SIG. In addition, the second legacy preamble indicates the HT preambleor VHT preamble. On the other hand, although not shown in FIG. 18, thelegacy packet may be an 11a/g packet, and in this case, thecorresponding packet may include only the first legacy preamble.

According to an embodiment of the present invention, at least one of thefirst legacy preamble and the second legacy preamble of the legacypacket transmitted by the non-legacy terminal may include non-legacyadditional information for the non-legacy terminal. If the legacy packetis an 11a/g packet, the non-legacy additional information may beincluded in the first legacy preamble. According to an embodiment of thepresent invention, the non-legacy additional information included in thelegacy preamble of the legacy packet may include at least one of thefollowing listed information.

1) Legacy mode (i.e., 11a/g/n/ac) indicator. First, the non-legacyadditional information may include the wireless LAN communicationstandard mode information used in the corresponding packet. When thenon-legacy additional information of the received packet indicates oneof legacy wireless LAN modes (e.g., 11a/g/n/ac), the non-legacy terminalmay omit or simplify the auto detection process for determining theformat of the received packet. For example, if the non-legacy additionalinformation indicates that the corresponding packet is an 11n packet,the non-legacy terminal receiving the packet may assume that thetransmission symbol configuration after the L-SIG is QBPSK+QBPSK, andimmediately perform reception and decoding processes. In addition, whenthe non-legacy terminal performs the auto detection process, it isverified in advance that the transmission symbol configuration of thecorresponding packet after the L-SIG is QBPSK+QBPSK, so that unnecessaryblind decoding processes may be omitted.

2) Preamble information for non-legacy terminals. Next, the non-legacyadditional information may further include preamble information for thenon-legacy terminal. In this case, the preamble information for thenon-legacy terminal may be represented through a combination of specificbit information not used in the legacy terminal among the legacypreambles. That is, the L-SIG of the first legacy preamble or the SIGinformation for the legacy terminals in the HT/VHT-SIG of the secondlegacy preamble may be maintained as it is, and represent preambleinformation for the non-legacy terminal through reserved bits in thecorresponding SIG.

3) Additional information for CCA operation of non-legacy terminal. Asdescribed above with reference to FIG. 17, the non-legacy terminal mayperform CCA using additional parameters. In this case, the non-legacyadditional information of the legacy packet may include a parameter forthe CCA operation of the non-legacy terminal, such as the BSS identifierinformation. The non-legacy terminal receiving the legacy packetaccording to the embodiment of FIG. 18 may determine the CCA thresholdvalue for the corresponding packet based on the BSS identifierinformation included in the non-legacy additional information of thecorresponding packet.

4) Bandwidth extension and channel allocation information. Finally, thenon-legacy additional information may include bandwidth extensioninformation or channel allocation information in order to support thenon-legacy terminal performing OFDMA transmission or transmissionthrough a continuous/non-continuous expanded bandwidth. For example, thenon-legacy AP may transmit downlink channel information usable byanother non-legacy STA through the non-legacy additional information ofthe legacy packet transmitted through a specific channel. In addition,the non-legacy STA may transmit a non-legacy packet through anotherchannel/band while transmitting a legacy packet through a specificchannel. In this case, information on another channel/band through whichthe non-legacy packet is transmitted may be included as the non-legacyadditional information of the legacy packet. AP receiving theinformation may simultaneously receive a legacy packet and a non-legacypacket based on the corresponding information.

According to an embodiment of the present invention, the legacy packettransmitted by the non-legacy terminal may include at least one of theabove-mentioned 1) to 4) as non-legacy additional information. Asdescribed in the embodiment of FIG. 17, the non-legacy additionalinformation may be represented by a predetermined bit of at least one ofthe first legacy preamble and the second legacy preamble of the legacypacket. In addition, the non-legacy additional information may berepresented by additional subcarrier(s) of at least one of the firstlegacy preamble and the second legacy preamble of the legacy packet.

Although the present invention is described by using the wireless LANcommunication as an example, the present invention is not limitedthereto and the present invention may be similarly applied even to othercommunication systems such as cellular communication, and the like.Further, the method, the apparatus, and the system of the presentinvention are described in association with the specific embodiments,but some or all of the components and operations of the presentinvention may be implemented by using a computer system having universalhardware architecture.

The detailed described embodiments of the present invention may beimplemented by various means. For example, the embodiments of thepresent invention may be implemented by a hardware, a firmware, asoftware, or a combination thereof.

In case of the hardware implementation, the method according to theembodiments of the present invention may be implemented by one or moreof Application Specific Integrated Circuits (ASICSs), Digital SignalProcessors (DSPs), Digital Signal Processing Devices (DSPDs),Programmable Logic Devices (PLDs), Field Programmable Gate Arrays(FPGAs), processors, controllers, micro-controllers, micro-processors,and the like.

In case of the firmware implementation or the software implementation,the method according to the embodiments of the present invention may beimplemented by a module, a procedure, a function, or the like whichperforms the operations described above. Software codes may be stored ina memory and operated by a processor. The processor may be equipped withthe memory internally or externally and the memory may exchange datawith the processor by various publicly known means.

The description of the present invention is used for exemplification andthose skilled in the art will be able to understand that the presentinvention can be easily modified to other detailed forms withoutchanging the technical idea or an essential feature thereof. Thus, it isto be appreciated that the embodiments described above are intended tobe illustrative in every sense, and not restrictive. For example, eachcomponent described as a single type may be implemented to bedistributed and similarly, components described to be distributed mayalso be implemented in an associated form.

The scope of the present invention is represented by the claims to bedescribed below rather than the detailed description, and it is to beinterpreted that the meaning and scope of the claims and all the changesor modified forms derived from the equivalents thereof come within thescope of the present invention.

Mode for Invention

As above, related features have been described in the best mode.

INDUSTRIAL APPLICABILITY

Various exemplary embodiments of the present invention have beendescribed with reference to an IEEE 802.11 system, but the presentinvention is not limited thereto and the present invention can beapplied to various types of mobile communication apparatus, mobilecommunication system, and the like.

1-20. (canceled)
 21. A wireless communication terminal comprising: atransceiver; and a processor, wherein the processor is configured to:receive, through the transceiver, a first preamble of a wireless packet,receive, through the transceiver, a second preamble of the wirelesspacket according to an identified configuration of the second preamble,wherein the configuration of the second preamble is identified based atleast in part on a detected constellation of a specific symbol of thesecond preamble, wherein when the detected constellation of the specificsymbol is a first constellation, the second preamble includes anHE-SIG-A field composed of four symbols, and wherein when the detectedconstellation of the specific symbol is a second constellation, thesecond preamble includes an HE-SIG-B field.
 22. The wirelesscommunication terminal of claim 21, wherein when the second preambleincludes an HE-SIG-A field composed of four symbols, a first symbol anda second symbol of the HE-SIG-A field has same data, and a third symboland a fourth symbol of the HE-SIG-A field has same data.
 23. Thewireless communication terminal of claim 21, wherein when the detectedconstellation of the specific symbol is the first constellation, theHE-SIG-A field is immediately followed by an HE-STF field of the secondpreamble.
 24. The wireless communication terminal of claim 21, whereinwhen the detected constellation of the specific symbol is the secondconstellation, the second preamble includes an HE-SIG-A field composedof two symbols immediately followed by the HE-SIG-B field.
 25. Thewireless communication terminal of claim 21, wherein the specific symbolis a third symbol after an L-SIG of the first preamble.
 26. The wirelesscommunication terminal of claim 21, wherein the second preamble includesa repeated L-SIG (RL-SIG) field composed of a first symbol of the secondpreamble, and wherein the specific symbol is a second symbol after theRL-SIG.
 27. The wireless communication terminal of claim 21, wherein thefirst constellation is quadrature binary phase shift keying (QBPSK) andthe second constellation is binary phase shift keying (BPSK).
 28. Thewireless communication terminal of claim 21, wherein the first preambleincludes a legacy short training field (L-STF), a legacy long trainingfield (L-LTF) and a legacy signal field (L-SIG).
 29. A wirelesscommunication method of a terminal, the method comprising: receiving afirst preamble of a wireless packet; and receiving a second preamble ofthe wireless packet according to an identified configuration of thesecond preamble, wherein the configuration of the second preamble isidentified based at least in part on a detected constellation of aspecific symbol of the second preamble, wherein when the detectedconstellation of the specific symbol is a first constellation, thesecond preamble includes an HE-SIG-A field composed of four symbols, andwherein when the detected constellation of the specific symbol is asecond constellation, the second preamble includes an HE-SIG-B field.30. The wireless communication method of claim 29, wherein when thesecond preamble includes an HE-SIG-A field composed of four symbols, afirst symbol and a second symbol of the HE-SIG-A field has same data,and a third symbol and a fourth symbol of the HE-SIG-A field has samedata.
 31. The wireless communication method of claim 29, wherein whenthe detected constellation of the specific symbol is the firstconstellation, the HE-SIG-A field is immediately followed by an HE-STFfield of the second preamble.
 32. The wireless communication method ofclaim 29, wherein when the detected constellation of the specific symbolis the second constellation, the second preamble includes an HE-SIG-Afield composed of two symbols immediately followed by the HE-SIG-Bfield.
 33. The wireless communication method of claim 29, wherein thespecific symbol is a third symbol after an L-SIG of the first preamble.34. The wireless communication method of claim 29, wherein the secondpreamble includes a repeated L-SIG (RL-SIG) field composed of a firstsymbol of the second preamble, and wherein the specific symbol is asecond symbol after the RL-SIG.
 35. The wireless communication method ofclaim 29, wherein the first constellation is quadrature binary phaseshift keying (QBPSK) and the second constellation is binary phase shiftkeying (BPSK).
 36. The wireless communication method of claim 29,wherein the first preamble includes a legacy short training field(L-STF), a legacy long training field (L-LTF) and a legacy signal field(L-SIG).